Composite metallic articles



Sept. 30, 1969 c. BAKER COMPOSITE METALLIC ARTICLES Filed March 14. 1967 FlG.2b. FIG. 2c.

FIG.20.

Fleze; FlG.2f.

FlG.2 d.

- 'INVYENTOR Colin Baker If evfiw, 24105 ATTORNEYSU' F ea.

United States Patent 3,469,952 COMPOSITE METALLIC ARTICLES Colin Baker, Richmond, Va., assignor to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Filed Mar. 14, 1967, Ser. No. 623,143

Int. Cl. B21c 37/00 U.S. Cl. 29191.4 12 Claims ABSTRACT OF THE DISCLOSURE Improving the fracture toughness of metals, by incorporating discrete elements of a ductile material. Techniques are presented for introducing wires or rods of the ductile material into a molten or solid matrix of a high strength aluminum base alloy, such as heat-treatable alloy 7075, to form a composite sheet or extruded shape.

BACKGROUND There has been a continuing and increasing interest in aluminum alloys of high strength for aircraft and related applications, but alloys of the aluminum-zinc-magnesium system (such as 7075 alloy), which are capable of attaining yield strengths above 65,000 p.s.i. in heat treated (T6) temper, have tended to exhibit inadequate fracture toughness. The toughness of an alloy depends on a combination of its ultimate tensile strength and the amount of deformation which the alloy undergoes before fracturing. The 7000 series aluminum base alloys ordinarily do not have a high fracture toughness due to their relatively low ductility in heat treated condition. Thus, the intrinsic strength of these alloys has not been fully realized in practice. Stress concentrations due to notches and similar discontinuities have reduced the design limits which can be safely employed.

In accordance with the present invention, however, incorporation of more ductile material in small amounts has been found to reduce the notch sensitivity of high strength 7000 series aluminum alloys and to increase the energy of propagation of any cracks which are initiated.

While fiber reinforcing of metals has been known previously, the purpose has usually been to incorporate reinforcing elements of greater strength than the metal matrix. In contrast, the present invention involves the use of weaker and more ductile elements in a highstrength matrix.

SUMMARY OF THE INVENTION The invention relates to composite articles of improved fracture toughness, particularly aluminous metal articles having a matrix of high-strength heat treatable aluminum alloy containing elongated elements of a more ductile material than the matrix alloy.

In accordance with the invention, a small but effective amount of the ductile material may be distributed in an aluminum alloy matrix to provide a composite article characterized by substantially the same strength, yet greater fracture toughness than the alloy itself. This may be accomplished in various ways such as, for example, by introducing wires or rods of the ductile material into the molten alloy during casting, and rolling the resulting composite into a wrought sheet product; by casting an extrusion billet of the alloy, drilling the billet to receive wires or rods of the ductile material, and extruding the resulting composite billet; or by compacting particles of the aluminum alloy in admixture with pieces of the ductile material to form a consolidated composite article.

The method of introducing such elements during casting is preferred when the elements have a sufiiciently high melting point compared to the matrix alloy; how ever, the other methods are useful for introducing mate- 5 rials of lower melting points. One advantage of inserting the elements within holes in a solid matrix is the precision of control alforded in distributing the elements within the matrix.

In the accompanying drawings:

FIG. 1 is a cross-sectional view of a drilled extrusion billet adapted for purposes of the invention to receive rods of more ductile material inserted in the drill holes;

FIGS. 2(a)-(f) show transverse sections at spaced positions along the length of an extrusion made from the billet of FIG. 1, as hereinafter discussed in connection with Example 3.

The ductile elements may be made of commercial purity aluminum, or an aluminum alloy which is more ductile and weaker than the matrix alloy, or any other material which is compatible with particular end uses of the composite. It is not essential even that the elements be metallic. In general, however, if the elements are to be introduced into the molten alloy, they should be composed of material having a melting point higher than that of the alloy; otherwise, supplemental cooling of the elements may be necessary. It is preferable, furthermore, in forming a composite having a heat-treatable matrix, to use elements composed of material which remains solid at the heat treating temperature.

The preferred material is alminous metal which is nearly all aluminum, such as 1100, 7072 or 6061 alloy, having suflicient strength to absorb the energy of a propagating crack. The proportion of ductile material may range up to about 30% by volume, preferably about 5 to 10%.

DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS The following examples are illustrative of the invention, and are not to be regarded as limiting:

Example 1 This method produces wrought sheet composites containing about 5% ductile material by volume, in the form of flattened ribbons:

7075 aluminum alloy was cast into a 5 pound book mold at 1,350-1,450 F. Wires of 7072 alloy, inserted in a thick support plate, were pushed down into the molten alloy. The 7072 wires in this case were 0.063" diameter, straightened in a tensile machine, and cut in lengths to fit the mold. The mold dimensions were 2" x 4" x 5 /2". A plain 7075 ingot without wires was also cast from the same melt to give a comparison for mechanical property determinations.

The resulting ingots were rolled to 0.25" thickness in passes of 0.125" reduction per pass, at an 800 F. starting temperature and with a reheat after each third pass.

This material was then machined to 0.2" thickness to remove any surface defects and tested, giving the following results based on an average of at least two specimens:

S# 16548, 7075 alloy without Wires.

S#16549, 7075 alloy with wires.

TENSILE TESTS Percent U.'I.S. t0. 2% EL (K s.i.) Offset) (1' G.L.)

NOTOHED TENSILE TESTS DRE-CRACKED CHARPY TESTS U.T.S. Total Energy to Energy/Unit area (K s.i.) Fracture (in. lbs.) Energy (in. lbs.) (m. 1b./sq. in.)

KAHN TEAR TESTS Tear Strength Total Energy ql0 S.E.N. FRAOTURE TOUGHNESS TESTS ish 73 6 404 16810- 50, 753 No valid K1 values could be obtained on the 16811 FEE-CRACKED CHARPY TESTS 16811. 53, 990 16813, or 16815 material because of plastic deforma- 16813. 61, 118 tion during the tests. This is an indication of good Energy/Unit area 168l5 59, 700 toughness. Energy (in. lbs.) (in. lbs/sq. in.)

Example 3 FRACTURE TOUGHNESS TESTS This illustrates a method of producing extruded shapes of 7075 alloy with longitudinal wires of weaker and more Kc K10 d (psi) Km ucti e material evenly spaced m the product. An 8 diameter 7075 extrusion billet 8" long was drilled with 60 lon- 36, 400 No valid K1 values could be obtained on the 16549 54,800 material because of the high plastic deformation during the tests. This is an indication of good toughness.

Example 2 Also prepared were sheet specimens with wires incorporated of round cross section which were reduced to a tape-like shape by rolling. The material was cast by the same technique as in Example 1 but in a 20 lb. book mold. Two wire sizes were used: 0.063" diameter 7072 alloy and 0.125" electrical conductivity (EC) aluminum. A plain 7075 alloy billet was also cast for comparison.

These materials were also hot rolled to 0.25 and both surfaces machined to a finished size of 0.2" thick.

S# 16810Plain 7075 alloy cast at 1,400 P.

S#1681l7075 alloy with 0.063" 7072 wires cast at 1,600 F.

S#168137075 alloy with 0.063" 7072 wires cast at 1,600 F.

S#168l57075 alloy with 0.125 EC aluminum wires cast at 1,500 F.

The test results were as follows:

NOTCHED TENSILE TESTS U.T.S.

(Ks.i.) Energy (in. lbs.)

gitudinal holes in diameter in a pattern shown in the attached FIGURE 1. A set of A" diameter EC rods were then placed in the holes and an end cap 3" long and 8" in diameter was welded to each end, and the weld bead machined oiT to give a finished composite billet 14" long and 8" diameter.

This billet was preheated at 800 F. for 8 hours and extruded through a 1% diameter 90 die. The front cap was provided in order to allow a conical dead metal die build up to form without disturbing the wires. This, however, caused the central ring of EC aluminum rods to appear first in the extruded bar (see FIG. 2a). As extrusion continued, successive rings of the softer wires appeared (FIGS. 2b, 2c) until all of the 60 rods could be seen in a cross-section of the extruded bar with about equal reduction in area (FIG. 2d). Similarly at the end of the extrusion the central wires were depleted first (FIG. 2e), and then the outer rings (FIG. 2 as the rear end cap entered the die. Consequently a variable product of between 0% and 7% EC aluminum was obtained from the same billet.

A central section of the extrusion (containing about 7% EC), having a length of about 4 feet, was then rod rolled to diameter and drawn to /2 diameter, thus providing specimens of three diameters, 1 /8", /8 and /2", in which the wire diameters were about 0.051, 0.020 and 0.016" respectively.

These materials gave the following properties when tested with plain 7075 alloy, in the T-6 temper:

S# 172071%" extruded cylindrical composite. S# 17209 /s dia. rolled rod. S#17210- /2 dia. drawn rod. S# 172081'%" dia. extruded 7075 (no inserts).

TENSILE TESTS Y.S. urnsuz s.i.) (K s.i.) Percent E1.(1.4) 68.9 434.0 S 5 9 17209 74. 3 64. 0 1e. 9 17210 7e. 0 65. 4 1s. 0

KAHN TEAR TESTS Tear Strength Total energy (in.

( s.i.) lb./sq.1n.) 70 NOTCHED TENSILE TESTS U.T.S.(K s.i.) Ener y (in.lb. 72.1 536 g 81.8 784 74.3 626 93.6 as) 73.4 581 93.8 352.

CHARPY TESTS Energy/Unit are 1 Avg. of 4 specimens giving min. of 7 50 "and max. of 1,600.

S.E.N. FRA-OTURE TOUGHNESS TEST S. No. 17207, K (p.s.i.), 47,800; S. No. 17208, K (p.s.i.), 51,200.

The above-mentioned tests were conducted in accordance with conventional procedures, based on the following standards: Tension tests-ASTM specification E8-65T.

Notched Tensile, Flat Sheet Specimens- ASTM Proceedings, Vol. 62,

1962, pages 778-791.

Notched Tensile, Round Specimens Materials Research and Standards, Vol. 2, No. 3, March, 1962, pages 196-204.

Kahn type Tear Tests, ASTM Materials Research and Standards, Vol. 4, page 151 Pre-Cracked Oharpy Tests Specifications in ASTM E 23 were followed except the specimens were precracked .050.

Km Test ASTM Special Technical Publication, No. 381, Fracture Toughness Testing and Its Applications, April, 1966, pages 133-196.

While present preferred embodiments of the invention have been described, it will be apparent that the invention may be otherwise variously embodied and practiced within the scope of the following claims.

What is claimed is:

1. An article comprising a composite body having an aluminum base alloy matrix containing discrete elements of a more ductile material embedded therein, in minor proportion by volume, said elements being effective to afford greater fracture toughness of the composite than if said body were made only of said matrix alloy.

2. An article according to claim 1, in which said ductile material has a higher melting point than said matrix alloy.

3. An article comprising a composite body in the form of a Wrought sheet having a metal matrix containing discrete elements of a more ductile material embedded therein, in minor proportion by volume, said elements being effective to aiford greater fracture toughness of the composite than if said body were made only of said matrix metal.

4. An article comprising a composite body in the form of an extruded shape having a metal matrix containing discrete elements of a more ductile material embedded therein, in minor proportion by volume, said elements being effective to afford greater fracture toughness of the composite than if said body were made only of said matrix metal.

5. An article comprising a composite body having a matrix composed of a heat-treatable aluminum base alloy in which zinc and magnesium are the principal alloying elements, containing discrete elements of a more ductile material embedded therein, in minor proportion by volume, said elements being effective to afford greater fracture toughness of the composite than if said body were made only of said matrix alloy.

6. An article according to claim 5, in which said elements are composed of aluminous metal of greater aluminum content than said alloy.

7. An article comprising a composite body having a Wrought matrix of heat-treatable aluminum base alloy, and a plurality of elongated elements of a more ductile material embedded within said matrix, in minor proportion by volume, the melting point of said material being high enough to permit heat treatment of the composite to effect strengthening of said matrix alloy, said elements being effective to aiford greater fracture toughness of the composite than if said body were made only of said matrix alloy.

8. An article according to claim 7, in the form of a wrought sheet in which said elements have a flattened ribbon-like configuration.

9. An article according to claim 7, in which said elements are composed of aluminous metal of greater aluminum content than said alloy.

10. An article according to claim 7, having a matrix composed of an aluminum base alloy in which zinc and magnesium are the principal alloying elements.

11. An article according to claim 7, having a matrix composed of aluminum base alloy 7075.

12. An article according to claim 7, comprising a composite body having aluminum alloy 7075 as the matrix with a plurality of commercially pure aluminum elements embedded therein, said elements constituting about 5 to 10% of the total composite.

References Cited UNITED STATES PATENTS 1,292,659 1/1919 Speed 29l9l.4

FOREIGN PATENTS 996,387 6/ 1965 Great Britain.

L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R. 

